
Hi Dennis Haschke, I want to help you with this question.
This is currently not possible with the Outlook client (client site). See also https://answers.microsoft.com/en-us/outlook_com/forum/all/mailbox-rule-based-on-specific-attachment-type/4c68bde5-f7a3-4d8f-904c-99424635fd18
But you can create rules on org level where could be filtered by the attachment extensions:
I hope this will answer your question.
If the reply was helpful, please don’t forget to upvote or accept it as an answer, thank you!